A plastic lens is lighter, more resistant to cracking and is dyed more easily than an inorganic type glass lens. In addition, an improvement in hardcoat techniques and the development of a resin material having a high refractive index have brought about the possibility of thinner and lighter lenses being produced. Plastic lenses in place of inorganic type glass lenses have been thereby spread in many fields of optical elements including glasses.
Plastic lens materials that have been most widely used are resins obtained by radical polymerization of allyl diglycol carbonate-(ADC). However, a resin material having a high refractive index has been developed in recent years. Typical examples of these resins include sulfur-containing plastic lens resins having a refractive index of 1.55 or more such as sulfur-containing urethane resins, sulfur-containing epoxy resins, polythio(meth)acrylate resins, sulfur-containing poly(meth)acrylate resins and episulfide resins.
A molding glass die is usually used for the production of a plastic lens. This molding glass die is cleaned after a lens is molded and used repeatedly many times. Examples of stains stuck to the molding glass die when molding a plastic lens include high-molecular weight resinous stains such as plastic lens molding raw materials, unreacted monomers, oligomers, polymers (resins), components bleeding out from gaskets, plasticizers, adhesives and removable adhesives derived from mold fixing tapes, fingerprints of operators and dusts in the atmosphere. Among these stains, plastic lens resins are highly crosslinked, secured very firmly to the mold and therefore is difficult to clean.
As detergents for molding glass die, for example, a detergent composition (JP-A 11-172300) containing an alkali agent, a specific surfactant, a calcium ion emitting material and water is currently known. This reference specifically discloses resins having a refractive index as low as 1.50 or less such as diethylene glycol bisallyl carbonate type plastic lens resins and urethane type resins which are currently mainstream cleaning subjects.